Exploring the action mechanism of magnesium in different cations sites for LiNi0.5Mn1.5O4 cathode materials

Micron-sized single-crystal LiNi0.5Mn1.5O4 (LNMO-900) cathodes suffer from poor rate capability and inferior specific capacity. Mg doping is regarded as an efficient strategy to improve the electrochemical performance of LNMO cathodes. In this work, the effect of replacing a small part of Ni or Mn with Mg are studied. Compared with LiNi0.47Mg0.03Mn1.5O4 (Mg–Ni-LNMO), the lattice parameter of LiNi0.5Mn1.47Mg0.03O4 (Mg–Mn-LNMO) is significantly increased, which provides a wider channel for the transmission of Li+. Besides, the Mg–Mn-LNMO has a higher Ni2+ and a lower Mn3+ content in the crystal lattice, which is beneficial to improve the energy density and cycling stability. Moreover, replacing Mn with Mg in LNMO effectively suppresses Jahn-Teller distortion and helps to alleviate the dissolution of transition metal elements, which improves the capacity retention, especially at high temperatures. Our research indicates that replacing a small part of Mn is more feasible to improve the cycle performance of LNMO cathodes.